Rocket Japanese is a pretty good introduction to Japanese. It's definitely far better than Rosetta Stone and a few other programs I had some experience with (but fortunately never actually wasted money on), but despite how they boast about teaching grammar, it does a woefully inadequate job of teaching even the most basic grammar, and there are some strange choices for vocabulary to teach: for instance, there is an entire survival kit that is more than 80% words that I will never use because I don't drink alcohol or eat pork or shrimp. That being said, when used alongside other resources, it can be a fantastic introduction to Japanese. I especially recommend Tangorin.com (a dictionary) as a vocab supplement and Tae Kim's "Guide to Japanese" for grammar.

I believe that the purpose to Rocket Japanese is to teach you enough of a language to be able to have some level of basic interaction with natives if you go to Japan. To actually be able to learn the language to any real degree of fluency, you'll need a lot more. Nihongonomori.com is a good place to go after completing Rocket Japanese if you want to keep going in your Japanese studies.